Lakes

Question 1

List the types of oxidation pond used for secondary treatment of wastewater

Answer 1

• Aerobic ponds,
• Anaerobic ponds,
• Maturation or tertiary ponds (polishing ponds);
• Aerated lagoons
• Facultative ponds

Question 2

outline the main features of facultative ponds.

Answer 2

Ponds 1 to 2.5 m deep, which have an anaerobic lower zone, a facultative middle zone, and an aerobic upper zone maintained by photosynthesis and reaeration.
They are the most common type selected as wastewater treatment system for small communities. Attributes: long retention times facilitate the management of large flow fluctuations; operating and maintains costs are less than that of other biological systems.

Question 3

nitrification

Answer 3

the conversion of organic nitrogen into nitrates in water by nitrifying bacteria, under aerobic conditions

Question 4

denitrification

Answer 4

the conversion of nitrates into nitrogen in water by denitrifying bacteria, under anaerobic conditions, nitrogen is lost to the atmosphere

Question 5

List the classified lakes based on their productivity

Answer 5

Ogliotrophic, Eutrophic, Mesotrophic, Senescent

Question 6

explain the classified lakes principal characteristics

Answer 6

Oligotrophic lakes have a low level productivity due to limited supply of nutrients.
Water is clear, euphotic zone extends to hypolimnion: it is aerobic. They support cold-water
fish.

Eutrophic lakes have a high productivity due to an abundant supply of nutrients. Highly
turbid water (algae), when algae die their decomposition in benthic zone can deplete the O2 of
hypolimnion, during summer stratification: it is anaerobic. They support warm-water fish and
often have unpleasant taste, and odour.

Mesotrophic lakes are intermediate between oligothrophic and euthrophic.
Hypolimnion is still aerobic.

Senescent lakes are very old, shallow, with rooted plants. They are to become
marshes

Question 7

Reverse Osmosis

Answer 7

is a separation process that uses pressure to force a solution through a
membrane that retains the solute on one side and allows the pure solvent to pass to the other side

Bacteria and ions (e.g. ions from inorganic minerals such as Arsenic, fluoride…) can be removed
from waters by reverse osmosis.